The dependence of annulate lamellae formation on the nucleus in parthenogenetic rabbit eggs

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Abstract
Previously it has been shown that, in the rabbit, although annulate lamellae (AL) are absent in the follicular oocytes, they appear in the fertilized eggs after the formation of the pronuclei. Furthermore, neither pronuclei nor AL appear when unfertilized eggs are aged in vivo or in vitro. This study was undertaken to determine whether AL formation requires presence of an intact nucleus, or whether the sperm alone contains the stimulatory factors essential to AL synthesis. Rabbit eggs were exposed to 10°C, then incubated for 24 hours. Control eggs were incubated without cold-treatment. Electron microscopic observations indicated that two-thirds of the eggs formed one or two ‘pronuclei,’ or subnuclei. The remainder one-third of the cold-treated eggs and the control eggs failed to form ‘pronuclei.’ AL were present in large amounts only in those activated eggs (parthenogenones) which formed ‘pronuclei.’ AL were absent in the control and the non-activated experimental eggs, both of which failed to form a ‘pronucleus.’ A few small AL were observed in eggs with subnuclei. Condensed fine textured nucleoli appeared precociously during cold-treatment in some eggs and they were present in the ‘pronuclei’ of activated eggs. It was concluded that the sperm is not necessary for AL formation, but the presence of an intact nucleus is mandatory.